Calculations Of Energy Surfaces Research Articles

HF Trimer: A New Full-Dimensional Potential Energy Surface and Rigorous 12D Quantum Calculations of Vibrational States.

HF trimer, as the smallest and the lightest cyclic hydrogen-bonded (HB) cluster, has long been a favorite prototype system for spectroscopic and theoretical investigations of the structure, energetics, spectroscopy, and dynamics of hydrogen-bond networks. Recently, rigorous quantum 12D calculations of the coupled intra- and intermolecular vibrations of this fundamental HB trimer (J. Chem. Phys. 2023, 158, 234109) were performed, employing an older ab initio-based many-body potential energy surface (PES). While the theoretical results were found to be in reasonably good agreement with the available spectroscopic data, it was also evident that it is highly desirable to develop a more accurate 12D PES of HF trimer. Motivated by this, here we report a new, and the first fully ab initio 12D PES of this paradigmatic system. Approximately 42,540 geometries were sampled and calculated at the level of CCSD(T)-F12a/AVTZ. The permutationally invariant polynomial-neural network based Δ-machine learning approach (J. Phys. Chem. Lett. 2022, 13, 4729) was employed to perform cost-efficient calculations of the basis-set-superposition error (BSSE) correction. By strategically selecting data points, this approach facilitated the construction of a high-precision PES with BSSE correction, while requiring only a minimal number of BSSE value computations. The fitting error of the final PES is only 0.035 kcal/mol. To assess its performance, the 12D fully coupled quantum calculations of excited intra- and intermolecular vibrational states of HF trimer are carried out using the rigorous methodology developed by us earlier. The results are found to be in a significantly better agreement with the available spectroscopic data than those obtained with the previously existing semiempirical 12D PES.

Structural, electronic, and optical-absorption properties of 2D Si thin films

AbstractRecent experimental studies highlighted the potential of thin-film crystalline silicon (Si) for high-efficiency solar cells. Using density functional theory, we investigated 2D Si thin films across various orientations, thicknesses, and surface structures to elucidate their structure–property relationships. Through surface-energy calculations and Wulff construction, we determined the crystal habit of Si, which aligns with available experimental observations. Electronic-structure calculations underscored the critical role of valence saturation on surfaces in enabling semiconducting behavior in Si thin films, essential for optical applications. From optical-absorption calculations, we identified the surface index exhibiting the highest absorption coefficients for thin films Si solar cell applications. Graphical abstract

First Principles Unveiling Equilibrium Shapes for Understanding Morphological Growth Mechanisms in Alumina Polymorphs

Understanding the morphological evolution of crystals is crucial for industrial applications and surface engineering. This study employs a multifaceted analytical approach to comprehensively analyze gibbsite, boehmite, η, γ, δ, θ, κ, and α-Al2O3. Density Functional Theory (DFT) surface energy calculations provide essential viewpoints into facet exposure and stability, enriching our comprehension of growth patterns. Using the Bravais–Friedel–Donnay–Harker (BFDH) method, a meticulous investigation into morphological properties reveals equilibrium shapes for each structure. Crucially, our models unveil the inaugural equilibrium shapes for structures previously undocumented in the literature (e.g., η, δ, θ, and κ-Al2O3). The study explores morphological growth process during phase transitions from gibbsite and boehmite to alpha alumina, emphasizing nucleation and dissolution preferences for specific facets. A grain analysis, considering bulk energy, surface area, and volume, designates α-Al2O3 as the most stable phase, offering valuable standpoints on thermodynamics and indicating a direct correlation between facet area and volume. Additionally, a comprehensive 3D surface energy mapping offers intricate visualization of facet interactions, providing valuable viewpoints into the complex relationships between surface energy, facet area, and interplanar distance. Comparisons of Fourier-transform infrared spectroscopy (FTIR) spectra, exclusively within the 200–400 cm-1 range, underscore close agreement between theoretical and experimental spectra, consistent with the expected reduction in specific surface area during polymorphic transformation.

Luminescent Mannich bases: Synthesis, crystal structures, and photophysical properties

Three Mannich bases have been obtained starting from 5-bromo-salicylaldehyde: 5-bromo-3-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde (TMEN), 5-bromo-3-((benzyl(methyl)amino)methyl)-2-hydroxybenzal-dehyde (MBA), 5-bromo-3-(ethyl(methyl)amino)methyl)-2-hydroxybenzaldehyde (EMA). The crystal structure of MBA has been solved. The UV-Vis absorption and emission spectra were investigated in different solvents, revealing the presence of several species, the neutral forms, the zwitterionic, the anionic and the cationic (the protonated nitrogen) ones. In order to characterize the last two species, further experiments were performed in the presence of hydrogen extracting and hydrogen donating compounds, sodium fluoride (NaF) and tetra butyl ammonium hydroxide (TBOH) to evidence the anion, and trichloroacetic acid (TCA) for the protonated cation. The experimental results were rationalized by DFT calculations of the potential energy surfaces (PES) of the S0 and S1 states and of the absorption and emission maxima.

Selenium Adsorption on the (111), (100), (110) and (211) Surfaces of Face‐Centered‐Cubic Metals: Density Functional Calculations of the Potential Energy Surfaces

AbstractIn this study, we expand the computational investigation of selenium, which has previously been limited to metals such as Cu, Fe, Pd, Au, and Pt. Utilizing density functional theory calculations, we explore the adsorption and diffusion of selenium at a low‐coverage regime of 0.25 ML on a broader range of metal surfaces, including Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au. Our results reveal that selenium exhibits a distinct preference for three‐fold or four‐fold high‐coordination sites on most studied surfaces. We further analyze the minimum energy diffusion pathways, demonstrating that the energy barrier for selenium's surface diffusion varies significantly based on the orientation and nature of the metal surfaces. Specifically, on (100) surfaces, selenium exhibits the highest diffusion energy, ranging from 0.60 eV in Au(100) to 1.12 eV in Pd(100). The diffusion behavior on (110) and (211) surfaces is also elaborated, emphasizing the unique trends observed compared to previously studied elements like sulfur. Importantly, this study is a new reference for future computational analyses, filling existing gaps by providing comprehensive data on selenium adsorption on various face‐centered cubic metal surfaces not previously reported.

Structure, morphology and surface properties of α-lactose monohydrate in relation to its powder properties

The particulate properties of α-lactose monohydrate (αLMH), an excipient and carrier for pharmaceuticals, is important for the design, formulation and performance of a wide range of drug products. Here an integrated multi-scale workflow provides a detailed molecular and inter-molecular (synthonic) analysis of its crystal morphology, surface chemistry and surface energy. Predicted morphologies are validated in 3D through X-ray diffraction contrast tomography. Interestingly, from aqueous solution fastest growth is found to lie along the b-axis, i.e. the longest unit cell dimension of the αLMH crystal structure reflecting the greater opportunities for solvation on the prism compared to the capping faces leading to their slower relative growth rates. The tomahawk morphology reflects the presence of β-lactose which asymmetrically binds to the capping surfaces creating a polar morphology. The crystal lattice energy is dominated by van der Waals interactions (between lactose molecules) with electrostatic interactions contributing the remainder. Predicted total surface energies are in good agreement with those measured at high surface coverage by inverse gas chromatography, albeit their dispersive contributions are found to be higher than those measured. The calculated surface energies of crystal habit surfaces are not found to be significantly different between different crystal surfaces, consistent with αLMH's known homogeneous binding to drug molecules when formulated. Surface energies for different morphologies reveals crystals with the elongated crystal morphologies have lower surface energies compared to those with a triangular or tomahawk morphologies, correlating well with literature data that the surface energies of the lactose carriers are inversely proportional to their aerosol dispersion performance.

The role of linkers and frustrated lewis pairs catalysts in the formation of zwitterionic 1,2-anti-addition product with non-conjugated terminal diacetylenes: A computational study

This study presents a computational investigation into the mechanistic pathway and the linker units involved in forming the zwitterionic 1,2-anti-addition product of non-conjugated diacetylenes, di(propargyl)ether (DPE), di(prop-2yn-1yl)sulfane (DPS) and 1,6-Heptadiyne (HD) catalyzed by the inter-molecular phosphine/borane frustrated Lewis pairs (FLPs), i.e., PPh2[C6H3(CF3)2](P-CF)/[B(C6F5)3]([B]) and P(o-tolyl)3(P-tol)/[B(C6F5)3]([B]). The potential energy surface (PES) calculations reveal that the anti-addition of P-CF to the internal C-atoms of acetylene units is energetically more favored than that of the addition of P-tol in DPE, DPS, and HD by ∼10.0, ∼9.2, and ∼6.0 kcal/mol, respectively. The calculations performed with DPE contain “—O—,” linker unit exhibits superior reactivity than DPS and HD, which suggests the electronegativity of linkers plays a significant role and facilitates the addition of Lewis bases. The higher electronegativity of linker units enables the 1,2-addition reaction by lowering the free energy activation barriers, as observed in the DFT calculations. The Molecular Electrostatic Potential (MESP) study shows that the electrostatic interactions favor the addition of P-CF to the active acetylene positions (C5/C4/C4) of [B]-DPE/DPS/HD-π complexes than the P-tol. The Distortion/Interaction (D/I) analysis reveals that transition states involving P-CF (TS1, TS3, and TS5) exhibit more interaction energy (ΔEInt) and less distortion energies (ΔEd) than that of the P-tol (TS2, TS4, and TS6). Further, the Energy Decomposition Analysis (EDA) also rationalizes the preferential approach of the electron-deficient Lewis base over the electron-rich one on the basis of the significant contribution of orbital interaction energies (ΔEorbital) in the cases of P-CF; TS1, TS3, and TS5. This study suggests that the electronic effects of substrates and the FLPs are crucial to facilitate the desired products formed with non-conjugated terminal alkynes.

Comparison of curvilinear coordinates within vibrational structure calculations based on automatically generated potential energy surfaces.

For floppy molecules showing internal rotations and/or large amplitude motions, curvilinear internal coordinates are known to be superior to rectilinear normal coordinates within vibrational structure calculations. Due to the myriad definitions of internal coordinates, automated and efficient potential energy surface generators necessitate a high degree of flexibility, supporting the properties arising from these coordinates. Within this work, an approach to deal with these challenges is presented, including key elements, such as the selection of appropriate fit functions, the exploitation of symmetry, the positioning of grid points, or elongation limits for different coordinates. These elements are tested for five definitions of curvilinear coordinates, with three of them being generated in an automated manner. Calculations for semi-rigid molecules, namely H2O, H2CO, CH2F2, and H2CNH, demonstrate the general functionality of the implemented algorithms. Additional calculations for the HOPO molecule highlight the benefits of these curvilinear coordinates for systems with large amplitude motions. This new implementation allowed us to compare the performance of these different coordinate systems with respect to the convergence of the underlying expansion of the potential energy surface and subsequent vibrational configuration interaction calculations.

Probing the Reaction of Propargyl Radical with Molecular Oxygen by Synchrotron VUV Photoionization Mass Spectrometry.

Self-reaction of propargyl (C3H3) radical is the main pathway to benzene, the formation of which is the rate-controlling step toward the formation of polycyclic aromatic hydrocarbons (PAHs) and soot. Oxidation of C3H3 is a promising strategy to inhibit the formation of hazardous PAHs and soot. In the present study, we studied the C3H3 + O2 reaction from 650 to 1100 K in a laminar flow reactor and identified the intermediates and products by synchrotron VUV photoionization mass spectrometry. 2-Propynal, ethenone, formaldehyde, CO, CO2, C2H2, C2H4, and C3O2 were identified. Among them, 2-propynal, ethenone, and formaldehyde provided direct evidence for the branching reaction of C3H3 + O2 → HCCCHO + OH, C3H3 + O2 → H2CCO + CHO, and C3H3 + O2 → H2CO + CHCO, respectively. Potential energy surface calculation and mechanistic analysis of the C3O2 formations implied that C3H3 + O2 → CCCHO + H2O and C3H3 + O2 → HCCCO + H2O could occur, despite lacking direct observations of CCCHO and HCCCO radicals. The formation of ethenone and CO suggested the occurrence of the two CO elimination channels. We incorporated these validated reactions and the corresponding rate coefficients in the kinetic model of NUIGMech1.3, and the simulation showed obvious improvements toward the measured mole fractions of C3H3 and H2CCO, suggesting that the new C3H3 + O2 reaction channels were crucial in the overall combustion modeling of the important intermediate propyne (C3H4).

Chemography-guided analysis of a reaction path network for ethylene hydrogenation with a model Wilkinson's catalyst.

Visualization and analysis of large chemical reaction networks become rather challenging when conventional graph-based approaches are used. As an alternative, we propose to use the chemical cartography ("chemography") approach, describing the data distribution on a 2-dimensional map. Here, the Generative Topographic Mapping (GTM) algorithm - an advanced chemography approach - has been applied to visualize the reaction path network of a simplified Wilkinson's catalyst-catalyzed hydrogenation containing some 105 structures generated with the help of the Artificial Force Induced Reaction (AFIR) method using either Density Functional Theory or Neural Network Potential (NNP) for potential energy surface calculations. Using new atoms permutation invariant 3D descriptors for structure encoding, we've demonstrated that GTM possesses the abilities to cluster structures that share the same 2D representation, to visualize potential energy surface, to provide an insight on the reaction path exploration as a function of time and to compare reaction path networks obtained with different methods of energy assessment.

Stress relief and crystal face transition process contribute to the stability of zinc anodes

Zn electrodes are suffering the dendrite growth owing to the enrichment of local space charge, distinct exposed face and residual stress. In this work, we investigated the crystal face properties and stress state of Zn foil through static energy calculations, dynamic crystal growth analysis and finite element simulation of stress states. Then thermal driven is deployed to modify the exposure face and residual stress of Zn foil, aiming for a dendrite-free electrode. The calculation of surface energies and simulation of crystal growth models for different crystal faces indicate that the (001) face can maintain stability during deposition. Inspired by this mechanism, the (101) exposed commercial Zn foil is modified by thermal processing. Firstly, the exposure level of the (001) face increases, though only the peak corresponding to the (002) crystal face is observed, due to the extinction effect of the densely packed plane (001) face. Further, the surface morphology becomes smooth and the stress is released with the progresses time. These stress relief and crystal face transition process strengthen the uniformity of ion distribution, and increase the interface stability during the crystal growth, which reduce the defect sites in the deposition. As a result, the Zn electrode exhibits tiny voltage hysteresis and outstanding cycle stability, which reveals improved electrochemical performance. Additionally, Li and Na can also be improved in exposed crystal faces and release strain energy through similar methods to enhance cycling stability.

Ab initio study of surfaces of lead and tin based metal halide perovskite structures

Abstract Hybrid perovskite materials, known for their potential in cost-effective optoelectronic applications, face a knowledge gap in crucial areas, particularly the atomic-level properties of the surface. This study addresses this challenge by refining ab initio methods for characterizing surface structures of cubic methylammonium lead bromide and methylammonium tin bromide (MAMeBr3 with Me = Sn, Pb), avoiding superficial restrictions in atomic movement during geometry optimization. The resulting structures confirmed nearly random MA+ molecule alignment, comparable to real-world experimental conditions. Calculating surface energies for these structures with crystal orientations {100} and {110}, each with different terminations, provides valuable insights into structural properties. Using a carefully chosen thermodynamic reference state, mimicking experimental conditions enables a thermodynamic discussion and facilitates the modulation of the MeBr2 component’s chemical potential. This modulation, in turn, allows for the prediction of crystal morphologies, as illustrated by Wulff’s construction. This approach establishes a crucial link between theoretical predictions and experimental conditions, shedding light on the complexities of hybrid perovskite materials.

Unveiling the enhanced hydrogen evolution performance of ternary heterostructures Mo5O14-Y(OH)3-CoMoO4/CF electrocatalysis

The challenge in electrocatalysis lies in finding stable and efficient catalysts for hydrogen evolution, especially those based on non-noble metals. Herein, the Mo5O14-Y(OH)3-CoMoO4/CF (CF stands for cobalt foam) catalyst rich in ternary heterostructures have been successfully synthesized. The catalyst is composed of cumin-like nanoparticles randomly dispersed on microcolumns. This unique structure ensures both its electrocatalytic activity and structural stability. Electrochemical tests demonstrate exceptional water splitting capabilities, with overpotentials of just 40 mV at 10 mA cm−2 (j10) and 219 mV at 1000 mA cm−2 (j1000). Furthermore, the catalyst shows minimal performance degradation after long-term testing, maintaining stable electrochemical performance for 60 h at j10 and 18 h at j800. Surface energy calculations and scanning electron microscopy (SEM) indicate that yttrium(Y) promotes the formation of cumin-like nanoparticles. Density functional theory (DFT) analysis, along with in situ Raman spectroscopy, suggests that the interaction among the three metals forms Mo5O14-Y(OH)3-CoMoO4 ternary heterostructures, effectively reducing the energy barrier for the hydrogen evolution reaction (HER). Notably, the Y sites in the CoMoO4-Y(OH)3 heterostructure exhibit the lowest hydrogen adsorption free energy (ΔGH⁎: −0.31 eV), making them the primary active sites for Mo5O14-Y(OH)3-CoMoO4/CF.

Performance Assessment of Universal Machine Learning Interatomic Potentials: Challenges and Directions for Materials' Surfaces.

Machine learning interatomic potentials (MLIPs) are one of the main techniques in the materials science toolbox, able to bridge ab initio accuracy with the computational efficiency of classical force fields. This allows simulations ranging from atoms, molecules, and biosystems, to solid and bulk materials, surfaces, nanomaterials, and their interfaces and complex interactions. A recent class of advanced MLIPs, which use equivariant representations and deep graph neural networks, is known as universal models. These models are proposed as foundation models suitable for any system, covering most elements from the periodic table. Current universal MLIPs (UIPs) have been trained with the largest consistent data set available nowadays. However, these are composed mostly of bulk materials' DFT calculations. In this article, we assess the universality of all openly available UIPs, namely MACE, CHGNet, and M3GNet, in a representative task of generalization: calculation of surface energies. We find that the out-of-the-box foundation models have significant shortcomings in this task, with errors correlated to the total energy of surface simulations, having an out-of-domain distance from the training data set. Our results show that while UIPs are an efficient starting point for fine-tuning specialized models, we envision the potential of increasing the coverage of the materials space toward universal training data sets for MLIPs.

Uncovering the hetero-hydrophobic attraction between the basal planes of molybdenite and talc under flotation conditions

The very close natural floatability of molybdenite and talc has been traditionally believed as the main reason for their separation problem. However, the interactions between the basal and edge planes of the two platy minerals remain unclear. Here the hydrophobic attraction between the basal planes was proposed as the dominating factor for that problem. Flotation tests in both single and mixed mineral systems were conducted using carboxymethyl cellulose (CMC) as talc depressant and sodium isobutyl xanthate (SIBX) as molybdenite collector. Zeta potential distribution, contact angle, in situ optical microscope observation, EDLVO calculation and surface energy analysis were applied to reveal the surfacial actions between the basal and edge planes of molybdenite and talc. Molybdenite and talc showed obvious floatability difference in single mineral system, however, their separation efficiency met with big decline in mixed mineral system. Zeta potential results demonstrated that, in the presence of CMC and SIBX, negatively charged particles of molybdenite and talc aggregated rather than electrostatically repulsed and dispersed. The contact angle and particle adhesion results showed a certain degree of selective attraction between the basal planes of molybdenite and talc. The EDLVO calculation suggested the attractive interactions were ranked as: Mb(basal)-Tlc(edge) > Mb(basal)-Tlc(basal) ≈ Mb(edge)-Tlc(edge) > Mb(edge)-Tlc(basal). The surface energy calculation pointed out that the fundamental reason for the separation problem was exactly the hetero-hydrophobic attraction between their basal planes.

Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH3, CH2, and CH Fragments.

Under irradiation of a vacuum ultraviolet (VUV) photon, methane dissociates and yields multiple fragments. This photochemical behavior is not only of fundamental importance but also with wide-ranging implications in several branches of science. Despite that and numerous previous investigations, the product channel branching is still under debate, and the underlying dissociation mechanisms remain elusive. In this study, the photofragment imaging technique was exploited for the first time to map out the momentum and anisotropy parameter distributions of the CH3, CH2, and CH fragments at the 118 nm photolysis wavelength (10.48 eV photon energy). In conjunction with previously reported results of the H atom fragment at 121.6 nm (10.2 eV), a complete set of product channel branching in both two-body and three-body fragmentations is accurately determined. We concluded that extensive nonadiabatic transitions partake in the processes with two-body fragmentations accounting for more than 90% of overall photodissociation, for which the channel branching values for CH2 + H2 and CH3 + H are about 0.66 and 0.25, respectively. Careful kinematic analysis enables us to untangle the intertwined triple fragmentations into the CH2(X̃ 3B1 and ã 1A1) + H + H and CH(X2Π) + H + H2 channels and to evidence their underlying sequential (or stepwise) mechanisms. With the aid of electronic correlation and prior theoretical calculations of the potential energy surfaces, the most probable or dominant dissociation pathways are elucidated. Comparisons with fragmentary reports in the literature on various photochemical aspects are also documented, and discrepancies are clarified. This comprehensive study benchmarks the VUV photochemistry of methane and advances our understanding of this important process.

Machine Learning Accelerates Precise Excited-State Potential Energy Surface Calculations on a Quantum Computer.

Electronically excited-state problems represent a crucial research field in quantum chemistry, closely related to numerous practical applications in photophysics and photochemistry. The emerging of quantum computing provides a promising computational paradigm to solve the Schrödinger equation for predicting potential energy surfaces (PESs). Here, we present a deep neural network model to predict parameters of the quantum circuits within the framework of variational quantum deflation and subspace search variational quantum eigensolver, which are two popular excited-state algorithms to implement on a quantum computer. The new machine learning-assisted algorithm is employed to study the excited-state PESs of small molecules, achieving highly accurate predictions. We then apply this algorithm to study the excited-state properties of the ArF system, which is essential to a gas laser. Through this study, we believe that with future advancements in hardware capabilities, quantum computing could be harnessed to solve excited-state problems for a broad range of systems.

Comparison of Inter-atomic Pair Potential Curves of different GEAM iterated values for Sr and Ir

In this study, the inter-atomic pair potential curve of Sr and Ir are compared with the potential curve of Rose et al. (1984) using the values predicted in our earlier study (The surface energy calculation for fcc metals with negative Cauchy’s discrepancy using the GEAM), utilizing an EAM model developed by Oni-Ojo et al. (2007) that ha demonstrated efficacy in predicting the low index surface energies of Sr and Ir, both of which have negative Cauchy’s discrepancy.

How to construct the most stable structure of (110) surface from rutile TiO2 bulk?

XRD pattern of rutile TiO2 bulk and surface energy of possible terminated (110) planes were investigated using the DFT+U method. The (110) surface was demonstrated to be the most popular facet of rutile TiO2, which is in good agreement with data of the JCPDS card No. 21-1276. The difference in surface energy among possible terminated (110) planes is attributed to structure of top and bottom atomic layers. We have found that the P5 plane is the most stable. It represents structure of (110) surface. Rutile TiO2 (110) surface has calculated surface energy of 0.98 J/m2. The value compares well with previous publications. Besides, DFT calculations were also performed. In comparison with DFT+U, surface energy obtained from DFT calculation for (110) surface is very small, about 0.48 J/m2.

Theoretical study of adsorption properties and CO oxidation reaction on surfaces of higher tungsten boride

Most modern catalysts are based on precious metals and rear-earth elements, making some of organic synthesis reactions economically insolvent. Density functional theory calculations are used here to describe several differently oriented surfaces of the higher tungsten boride WB5-x, together with their catalytic activity for the CO oxidation reaction. Based on our findings, WB5-x appears to be an efficient alternative catalyst for CO oxidation. Calculated surface energies allow the use of the Wulff construction to determine the equilibrium shape of WB5-x particles. It is found that the (010) and (101) facets terminated by boron and tungsten, respectively, are the most exposed surfaces for which the adsorption of different gaseous agents (CO, CO2, H2, N2, O2, NO, NO2, H2O, NH3, SO2) is evaluated to reveal promising prospects for applications. CO oxidation on B-rich (010) and W-rich (101) surfaces is further investigated by analyzing the charge redistribution during the adsorption of CO and O2 molecules. It is found that CO oxidation has relatively low energy barriers. The implications of the present results, the effects of WB5-x on CO oxidation and potential application in the automotive, chemical, and mining industries are discussed.